The present invention relates generally to improvements in portable combustion powered fastener driving tools, and specifically to improvements relating to the suspension of a motor for a combustion chamber fan for decreasing the operationally-induced axial acceleration and oscillation of the motor to decrease wear and tear on the motor.
Portable combustion powered, or so-called IMPULSE(copyright) brand tools for use in driving fasteners into workpieces are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722, 5,197,646 and 5,263,439, all of which are incorporated by reference herein. Similar combustion powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE(copyright) brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides for both an efficient combustion within the chamber, and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or xe2x80x9creadyxe2x80x9d position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly and the penetration of the fastener into the workpiece if the fastener is present. This combined downward movement causes a reactive force or recoil of the tool body. Hence, the fan motor, which is suspended in the tool body, is subjected to an acceleration opposite the power stroke of the piston/driver blade and fastener.
Then, within milliseconds, the momentum of the piston/driver blade assembly is stopped by the bumper at the opposite end of the cylinder and the tool body is accelerated toward the workpiece. Therefore, the motor and shaft are subjected to an acceleration force which is opposite the direction of the first acceleration. After experiencing these reciprocal accelerations, the motor oscillates with respect to the tool.
Conventional combustion powered tools of the IMPULSE(copyright) type require specially designed motors to withstand these reciprocal accelerations of the shaft and motor, and the resulting motor oscillations. Among other things, the motors are equipped with internal shock absorbing bushings, thrust and wear surfaces, and overall heavier duty construction. Such custom modifications result in expensive motors which increase the production cost of the tools. Thus, there is a need for a motor suspension mechanism for a combustion powered tool which reduces operating demands on the motor, increases reliability of the motor, and allows the use of standard production fan motors to reduce the tool""s production cost.
Accordingly, it is an object of the present invention to provide an improved combustion powered tool with an improved suspension mechanism for a combustion chamber fan motor which reduces operationally-induced reciprocal accelerations of the motor while keeping the oscillations of the motor within an acceptable range.
Another object of the present invention is to provide an improved combustion powered tool which features a mechanism for dampening operationally-induced oscillation of the combustion chamber fan motor.
A further object of the present invention is to provide an improved combustion powered tool having a suspension mechanism for a combustion chamber fan motor which allows for the use of a more standard, cost-effective motor.
It is yet another object of the present invention to provide an improved combustion powered tool having a suspension mechanism for a combustion chamber fan motor which increases the life of the motor.
The above-listed objects are met or exceeded by the present improved combustion powered fastener tool, which features a mechanism for suspending a combustion chamber fan motor that reduces the effects of the reciprocal axial acceleration of the motor, and the resulting oscillation of the motor, during operation of the tool. In the preferred embodiment, the assembly includes a flexible rubber web vulcanized to a motor retaining ring. The web is also vulcanized to a cylinder head mounting bracket so that only the web secures the ring to the bracket. The web is thinner in the middle than the radial inner and outer portions, and has a number of bores extending at least partially through the middle portion. As such, the present motor suspension mechanism is more flexible than conventional mechanisms. It has been found that a suspension mechanism which is more flexible, yet tuned to the input dynamics, significantly reduces and dampens accelerations and oscillations.
More specifically, the present invention provides a suspension mechanism for a motor of a combustion chamber fan in a combustion powered hand tool constructed and arranged for driving a driver blade to drive a fastener into a work piece, the tool generating an upward axial acceleration of the motor upon a combustion in the chamber, a subsequent reciprocal axial acceleration of the motor when the piston bottoms out on the bumper, and at least one of the accelerations causes the motor to oscillate relative to the tool. The present suspension mechanism is tuned for at least one of reducing the axial acceleration of the motor and dampening the oscillation of the motor relative to the tool.
The web of the present invention preferably has an upper surface with a number of bores and a lower surface with an undercut annular groove. The suspension mechanism limits the two axial accelerations experienced by the motor, during combustion and piston/bumper contact, to no more than about 50 g and dampens the subsequent oscillations of the motor to no additional oscillations with accelerations greater than about 25 g.